Lab 9 - Platyhelminthes and Nematoda

Define Auricle:

chemosensory organs that detect dissolved chemicals

Define Pharynx:

tubular, muscular extension of gastrovascular cavity used for ingesting food

Define Acoelomate:

animals whose central space is filled with tissue; lacking a body cavity

Define Monoecious

organism that contains both male and female reproductive structures

List several features of planaria that suggest adaptation to a free-living lifestyle

Cephalization and sensory structures such as eyespots and auricles; reduced cuticle, more body space devoted to digestion and less to reproduction; lack of hooks, suckers, or other structures for attaching to host

Why do you suppose the pharynx is centrally located on the body, as opposed to being located at the anterior end of the animal?

Its central location in the body permits a uniform delivery of nutrients to all portions of the body—a necessary consequence of not having a circulatory system to transport nutrients from the digestive system throughout the body

Why is the gastrovascular cavity so extensively branched?

Extensive branching increases the digestive surface area of the gastrovascular cavity and thus increases the efficiency of the digestive process and the delivery of nutrients to the surrounding cells.

Flatworms were the first organisms to evolve specialized cells for excretion (flame cells). What specific purpose does an excretory system serve?

It rids the body of cellular wastes and plays a significant role in osmoregulation by concentrating toxic metabolic by-products and channeling them out of the body, while conserving water

List several anatomical and behavioral features of trematodes that suggest adaptation to a parasitic lifestyle.

Anatomical: 

• Monoecious

• Extensive Rep Sys

• Reduced Digestive Sys

• Cuticle

• Suckers for attachment

• Lack of Sensory Structures

Behavioral:

• Ability to self-fertilize

• Huge Reproductive Potential

• Absorb body fluids from Host

• Resist Digestion by Host Enzymes

Which organs occupy the majority of the body space of the fluke? Explain

Rep Organs. Internal parasites absorb predigested nutrients and rely on diffusion for gas exchange and waste, so they lack complex organ systems. Low mating chances and offspring survival drive them to devote most of their body to reproduction.

Is the digestive system of flukes complete or incomplete?

Incomplete

What are the two intermediate larval stages in the life cycle of flukes?

Cercaria and Miracaidium

What defensive provision do flues possess for protection against the digestive enzymes of their hosts?

The cuticle, which is resistant to the digestive enzymes of its host

Describe the changes that occur in tapeworm proglottids as they mature

As tapeworm proglottids mature, they are shifted toward the rear of the body and gradually increase in size. Male first, female next.

Why is there an entire reproductive system in each proglottid?

allows each proglottid to reproduce independently and maximizes the overall reproductive output of the tapeworm

Tapeworms have been shaped by evolution for one purpose – reproduction. Describe how their body plan is set up to maximize their efficiency for obtaining nutrition and translating this energy into reproductive output

Their reduced organ systems leave more space for reproduction. Each proglottid acts as an independent reproductive unit, capable of self-fertilization and producing thousands of eggs. Mature proglottids detach and exit with feces, while the hardy eggs survive extreme conditions until development is possible.

Are the paths of flatworms straight or meandering? Explain why.

Meandering because in absence of a stimulus, they move forward in a winding indirect manner. 

Does the path of the flatworms change after adding the egg yolk?

They typically move towards it.

What sensory structures do the flatworms use to detect the presence of egg yolk?

Auricles

What response does the animal exhibit (to light)? Why? (flatworms)

They quickly recoil and attempt to avoid the bright light, because planaria typically show a systematic aversion to bright light.

How does it react (to light from the side)? Why? (Flatworms)

Again, they move away from the light because of their aversion to bright light

What conclusions can you make about their response to bright light?

Planaria attempt to avoid bright light caused by direct illumination

From your data on direct illumination where would you predict that the animals will aggregate in such a dish, and why? (Flatworms)

On the dark, shaded portion of the dish, because previous observations suggest that planaria show an aversion to brightly illuminated areas

Would you expect headless flatworms to respond differently? Why?

Headless flatworms would not be able to distinguish light areas from dark areas and should be randomly distributed throughout both sides of the dish.

Can you detect the rhythmic beating of cilia on each of the two halves of the corona? Do the cilia on the two halves beat in the same direction, or opposite directions?

Yes, rhythmic beating of the cilia is observable. The cilia on the two halves beat in opposite directions

Corona with cilia on head

P. Rotifera

what is A?

Triradiate lips around mouth.

List two external differences between male and female nematodes.

Males will generally be (1) smaller, (2) thinner, and (3) have a curved posterior end bearing small spicules.

Is the intestine surrounded by an outer layer of muscle? (Nematoda)

No

Why do you suppose the digestive system of nematodes is rather unspecialized?

Because the organic products that nematodes ingest require little additional digestion to access their nutrients.

Do nematodes fit the pattern typical of parasites, in that a large portion of their body cavity is devoted to reproductive structures?

Yes

Through what structures are male gametes released? (Nematoda)

Ejaculatory duct through anus (or cloaca)

Through which structure are females’ fertilized eggs released?

Genital pore

Identify!!!

Phylum Platyhelminthes. Class Turbellaria. Dugesia. 

Identify!!!

Phylum Platyhelminthes. Class Trematoda. Clonorchis.

Identify!!!

Phylum Platyhelminthes. Class Cestoda. Taenia.

Identify!!!

Phylum Nematoda. Ascaris

Identify!!! They move in Thrashing motions. 

Phylum Nematoda. Turbatrix. 

Identify!!!

Phylum Rotifera. Philodina.

Label.

Dugesia c.s.

We can find flame cells in …

Dugesia. Class Turbellia. Phylum Platyhelminthes. 

excretory and osmoregulatory cells that function like kidneys for the flatworm

Label and Name

Clonorchis. Class Trematoda. Phylum Platyhelminthes.

Label and Name

Phylum Platyhelminthes. Class Cestoda. Taenia.

Strobila - segments. Gravid proglottid - final egg filled segments.

Label and Name

Phylum Platyhelminthes. Class Cestoda. Taenia.

Label and Name

Phylum Nematoda. Ascaris

Label and Name

Phylum Nematoda. Ascaris

Label and Name

Phylum Nematoda. Ascaris

Label and Name

Phylum Rotifera. Philodina

Label X and Y. What is the function of Y? What is this organism?

X - Pharynx 

Y - Auricle

Chemoreception.

Dugesia. Phylum Platyhelminthes. Class Turbellaria.

Identify structure “V”. Name the space at “W”. Name this animal. 

V - Uterus

W - Pseudocoel

Phylum Nematoda. Class Cestoda. Ascaris c.s.

What is the body region shown?

Scolex. 

The wheel-like organ bearing cilia at the front end is the

Corona